The present invention relates to a method and an apparatus for coding digital image signals, a method and an apparatus for decoding coded digital image signals, and data recording media containing programs for making a computer execute coding processing and decoding processing of digital image signals and, more particularly, to time/space hierarchical coding processing of an image of an object having the arbitrary shape, and time/space hierarchical decoding processing corresponding thereto.
In order to store/transmit digital image information with good efficiency, it is required to perform compressive coding to the digital image information and, in the present circumstances, there are Discrete Cosine Transformation (DCT) which is representative in JPEG (Joint Photographic Coding Experts Group) and MPEG (Moving Picture Experts Group), and waveform coding methods such as subband, wavelet and fractal, as methods for compressively coding the digital image information.
As a method for removing redundant image information between adjacent pictures such as frames, there is a method of performing inter-picture prediction using motion compensation, that is, representing pixel values of pixels of the present picture using a difference between these pixel values and pixel values of pixels of the previous picture, and performing waveform coding to this difference signal.
Recently, in order both to improve compression efficiency and to regenerate an image signal for each of regions constituting one picture and corresponding to individual objects (hereinafter referred to as image spaces), a method of compressively coding an image signal object by object and transmitting the resulting signal has been made practicable. In this method, at the side of regeneration, coded image signals corresponding to individual objects are decoded, images of the individual objects regenerated by decoding are composed, thereby displaying an image corresponding to one picture. In this way, object-by-object coding of an image signal enables images of objects to be displayed to be freely combined and composed, whereby moving pictures can be easily reedited. Further, in this method, according to the congestion conditions of channels, the performance of a regenerative apparatus, and the viewer""s taste, moving pictures can be displayed without regenerating images of relatively unimportant objects.
More specifically, as methods for coding an image signal for forming image space including an image of an object having the arbitrary shape (hereinafter referred to as an object image), there are conventionally a coding method using a transformation method adaptive for its shape (for example, shape adaptive discrete cosine transformation), and a coding method of padding pixel values of pixels constituting an invalid region of an image space (that is, an outside region of an object image) by a specified method, and then performing cosine transformation to an image signal comprising plural pixel values corresponding to the image space, for each of unit regions into which the image space is divided (blocks comprising 8xc3x978 pixels).
As a specific method for removing a redundant signal between pictures such as frames, there is a method of using macroblocks comprising 16xc3x9716 pixels as unit regions, obtaining a difference between an image signal corresponding to a target macroblock as a target of coding processing and its prediction signal. Herein, the prediction signal is an image signal corresponding to a prediction region which is obtained by motion compensation. The motion compensation is processing of detecting a region comprising 16xc3x9716 pixels, the region providing an image signal having the smallest difference with the image signal of the target macroblock, in a picture which has been subjected to coding processing or decoding processing, as the prediction region.
However, when this prediction region is located at the boundary of the object image in the image space, the prediction region includes pixels with insignificant (undefined) sample values (pixel values). Therefore, concerning this prediction region, the corresponding image signal is subjected to padding processing in which the insignificant sample values are replaced with significant pseudo sample values, and a difference between the prediction signal which has been subjected to the padding processing and the image signal of the target macroblock is obtained as a prediction error signal (difference signal), and converting processing for coding is performed to the difference signal. Herein, the padding processing is executed to the prediction region for the purpose of suppressing the difference signal, i.e., reducing code quantity when the difference signal is coded.
In addition, there is a hierarchical processing method, which is called scalability, in which image signals corresponding to plural hierarchies having different resolutions are used as an image signal corresponding to each object, i.e., an image signal for forming image space including an object image, and the image signals of the respective hierarchies are coded to be decoded.
In such a hierarchical processing method, part of a bit stream that is extracted from transmitted data (coded bit stream) is decoded to regenerate an object image having low resolution, and all data is decoded to regenerate an object image having high resolution.
In the hierarchical coding (scalability coding) processing, an image signal corresponding to a high-resolution image (high-resolution image signal) is coded on the basis of an image signal corresponding to a low-resolution image (low-resolution image signal). That is, a high-resolution image signal corresponding to a target block as a target of coding processing is predicted using a corresponding low-resolution image signal to generate a predicted image signal, and a difference signal obtained by subtracting the predicted image signal from the high-resolution image signal of the target block, is coded.
When an image signal is coded object by object, a shape signal indicating the arbitrary shape of an object, together with a texture signal including a luminance signal and a color-difference signal for gradation color display of an object image, is coded as the image signal. Therefore, in performing scalability coding to the image signal corresponding to each object, it is necessary that not only the texture signal but the shape signal is separated into a high-resolution signal and a low-resolution signal to be hierarchically coded.
In this object-by-object scalability coding, it is required to predict a high-resolution texture signal from a low-resolution texture signal with good efficiency. Since, especially, a low-resolution texture signal corresponding to a macroblock located at the boundary of an object includes insignificant (undefined) sample values (pixel values), if this low-resolution texture signal is used as it is to generate a prediction signal and the prediction signal is subtracted from a high-resolution texture signal of a target macroblock as a target of coding processing, difference pixel values in a difference signal corresponding to the pixels located at the boundary of the object become large values, failing to code the high-resolution texture signal with good efficiency.
Further, since a shape signal is separated correspondingly to plural hierarchies having different resolutions, more specifically, a high-resolution hierarchy and a low-resolution hierarchy, there occurs disagreement of the boundaries indicating the inside and the outside of the object (outlines of the object), of the object shape obtained from the low-resolution shape signal and the object shape obtained from the high-resolution shape signal. This is because, by down-sampling processing in generating the low-resolution shape signal from the high-resolution shape signal, the shape of the object image of the low-resolution shape signal is transformed with respect to the shape of the object image of the high-resolution shape signal, and the object shapes of both the shape signals also are transformed by compression processing to the high-resolution shape signal and the low-resolution shape signal.
In this case, while a specified macroblock region in image space formed by a high-resolution texture signal is included in an object image, the specified macroblock region in image space formed by a low-resolution texture signal is wholly located outside the object image. In such a condition, even if a prediction signal of the high-resolution texture signal on the basis of the low-resolution texture signal is used, it is impossible to suppress a difference signal between the high-resolution texture signal and its prediction signal with good efficiency.
The present invention is subjected to solving the above-mentioned problems, and has an object to provide a digital image coding method and a digital image coding apparatus in which, on the basis of an image signal for forming image space including an image of an object having the arbitrary shape, image signals corresponding to plural hierarchies having different resolutions are generated and, in hierarchical coding processing of performing difference coding of a high-resolution image signal using a low-resolution image signal, to each of unit regions, the image signal of the unit region located at the boundary of the object can be compressed with good coding efficiency.
Another object of the present invention is to provide a digital image decoding method and a digital image decoding apparatus in which a coded image signal obtained by hierarchical coding processing that can compress an image signal for forming image space including an image of an object with good coding efficiency, can be accurately regenerated by corresponding hierarchical decoding processing.
Still another of the present invention is to provide data recording media containing programs for realizing the hierarchical coding processing in the digital image coding method and the hierarchical decoding processing by the digital image decoding method, using computers.
According to the present invention (claim 1), a digital image coding method for coding first and second input image signals having different resolutions, each signal forming image space including an image having the arbitrary shape and comprising plural pixels, includes performing coding processing to each of unit regions into which the image space is divided, in which coding processing the first input image signal is compressively coded to generate a first coded image signal, and the compressed first input image signal is expanded to generate a first regenerative image signal; performing padding processing in which insignificant pixel values are replaced with pseudo pixel values obtained by a specified method, to the first regenerative image signal corresponding to each unit region, and predicting the second input image signal corresponding to each unit region on the basis of the first regenerative image signal which has been subjected to the padding processing, to generate a prediction signal; and performing difference coding processing to each of unit regions, in which coding processing a difference signal that is a difference between the second input image signal corresponding to each unit region and its prediction signal is compressively coded to generate a coded difference signal, and the compressed difference signal is expanded and the prediction signal is added to the expanded difference signal, to generate a second regenerative image signal.
In the image coding method thus constructed, since the prediction signal of the second input image signal is generated on the basis of the first regenerative image signal which has been subjected to padding processing, the difference signal which is the difference between the second input image signal having the resolution different from that of the first input image signal and its prediction signal is suppressed, whereby the second input image signal corresponding to the unit region located on the boundary of the object can be compressed with suppressing degradation of coding efficiency.
Further, since, in coding processing of the second input image signal of the target unit region as a target of coding processing, a signal which is generated on the basis of the first regenerative image signal of the target unit region is used as its prediction signal, the coding processing of the second input image signal merely delays by time for processing the unit region, as compared with coding processing of the first input image signal. Therefore, at the side of decoding, on the basis of the first and second coded image signals which are obtained by coding the first and second input image signals, a high-resolution image and a low-resolution image can be regenerated almost without a time lag.
According to the present invention (claim 2), in a digital image coding method as defined in claim 1, the padding processing of the first regenerative image signal corresponding to each unit region comprises replacing the insignificant pixel values in the first regenerative image signal with pseudo pixel values obtained on the basis of significant pixel values in the first regenerative image signal.
In the image coding method thus constructed, since the padding processing of the first regenerative image signal corresponding to each unit region is performed on the basis of the significant pixel values in the first regenerative image signal, the difference between the prediction signal of the second input image signal which is obtained from the first input image signal and the second input image signal can be effectively suppressed.
According to the present invention (claim 3), a digital image coding apparatus comprises a first coding unit for coding a first input image signal for forming image space including an image having the arbitrary shape and comprising plural pixels; and a second coding unit for coding a second input image signal having different resolution from that of the first input image signal, for forming image space including the image and comprising plural pixels; wherein the first coding unit includes first coding means for performing coding processing to each of unit regions into which the image space is divided, in which coding processing the first input image signal is compressively coded to generate a first coded image signal, and the compressed first input image signal is expanded to generate a first regenerative image signal; and padding means for performing padding processing in which insignificant pixel values are replaced with pseudo pixel values obtained by a specified method, to the first regenerative image signal corresponding to each unit region; and the second coding unit includes prediction signal generating means for predicting the second input image signal corresponding to each unit region on the basis of the first regenerative image signal which has been subjected to the padding processing, to generate a prediction signal; and second coding means for performing difference coding processing to each of unit regions, in which coding processing a difference signal between the second input image signal corresponding to each unit region and its prediction signal is compressively coded to generate a coded difference signal, and the compressed difference signal is expanded and the prediction signal is added to the expanded difference signal, to generate a second regenerative image signal.
In the image coding apparatus thus constructed, since the prediction signal of the second input image signal is generated on the basis of the first regenerative image signal which has been subjected to padding processing, the difference signal which is the difference between the second input image signal having the resolution different from that of the first input image signal and its prediction signal is suppressed, whereby the second input image signal corresponding to the unit region located on the boundary of the object can be compressed with suppressing degradation of coding efficiency.
Further, since, in coding processing of the second input image signal of the target unit region as a target of coding processing, a signal which is generated on the basis of the first regenerative image signal of the target unit region is used as its prediction signal, the coding processing of the second input image signal merely delays by time for processing the unit region, as compared with coding processing of the first input image signal. Therefore, at the side of decoding, on the basis of the first and second coded image signals which are obtained by coding the first and second input image signals, a high-resolution image and a low-resolution image can be regenerated almost without a time lag.
According to the present invention (claim 4), a digital image coding apparatus as defined in claim 3 further includes resolution converting means for converting the first regenerative image signal which has been subjected to the padding processing so that its resolution agrees with that of the second input image signal, and outputting a resolution converting signal; wherein the prediction signal generating means comprises prediction means for predicting the second input image signal corresponding to each unit region on the basis of the second regenerative image signal to generate an auxiliary prediction signal; and switching means for performing switching between the auxiliary prediction signal and the resolution converting signal on the basis of control information included in the second input image signal; and the output of the switching means is output as the prediction signal of the second input image signal corresponding to each unit region.
In the image coding apparatus thus constructed, since one of the auxiliary prediction signal obtained from the second input image signal and the resolution converting signal obtained from the first input image signal is selected on the basis of the control information included in the second input image signal, and the selected signal is output as the prediction signal of the second input image signal corresponding to each unit region, the prediction signal can be adaptively switched by the simple construction, whereby coding efficiency in hierarchical coding processing can be more enhanced.
According to the present invention (claim 5), a digital image coding apparatus as defined in claim 3 further includes resolution converting means for converting the first regenerative image signal which has been subjected to the padding processing so that its resolution agrees with that of the second input image signal, and outputting a resolution converting signal; wherein the prediction signal generating means comprises prediction means for predicting the second input image signal corresponding to each unit region on the basis of the second regenerative image signal to generate an auxiliary prediction signal; and averaging means for weighting and averaging the auxiliary prediction signal and the resolution converting signal; and the output of the averaging means is output as the prediction signal of the second input image signal corresponding to each unit region.
In the image coding apparatus thus constructed, since the auxiliary prediction signal obtained from the second input image signal and the resolution converting signal obtained from the first input image signal are weighted and averaged, and the averaged signal is output as the prediction signal of the second input image signal corresponding to each unit region, the difference value between the prediction signal of the second input image signal obtained from the first regenerative image signal and the second input image signal can be finely controlled, whereby coding efficiency in hierarchical coding processing can be improved.
According to the present invention (claim 6), in a digital image coding apparatus as defined in claim 5, the padding means is for performing padding processing in which the insignificant pixel values in the first regenerative image signal are replaced with pseudo pixel values obtained on the basis of significant pixel values in the first regenerative image signal.
In the image coding apparatus thus constructed, since the padding processing of the first regenerative image signal corresponding to each unit region is performed on the basis of the significant pixel values in the first regenerative image signal, the difference between the prediction signal of the second input image signal obtained from the first input image signal and the second input image signal can be effectively suppressed.
According to the present invention (claim 7), in a digital image coding apparatus as defined in claim 3, the first coding means comprises an operator for obtaining a difference between the first input image signal corresponding to each unit region and its prediction signal and outputting a difference signal; a compressor for compressing the difference signal; an encoder for coding the compressed difference signal; an expander for expanding the compressed difference signal; an adder for adding the output of the expander to the prediction signal of the first input image signal, and outputting a first regenerative image signal to the padding means; a frame memory for storing the output of the padding means; and a prediction signal generator for generating the prediction signal of the first input image signal corresponding to each unit region, on the basis of the first regenerative image signal which has been subjected to the padding processing, which image signal is stored in the frame memory.
In the image coding apparatus thus constructed, since the first regenerative image signal which has been subjected to padding processing is stored in the frame memory, motion detection and motion compensation can be executed with good precision.
According to the present invention (claim 8), a digital image decoding method for decoding first and second coded image signals which are obtained by performing coding processing to first and second image signals having different resolutions, each signal forming image space including an image having the arbitrary shape and comprising plural pixels, to generate first and second regenerative image signals, includes performing decoding processing in which a first regenerative image signal is generated from the first coded image signal, to each of unit regions into which the image space is divided; performing padding processing in which insignificant pixel values are replaced with pseudo pixel values obtained by a specified method, to the first regenerative image signal corresponding to each unit region, and predicting a second regenerative image signal corresponding to each unit region on the basis of the first regenerative image signal which has been subjected to the padding processing, to generate a regenerative prediction signal; and performing difference decoding processing to each of unit regions, in which decoding processing the second coded image signal corresponding to each unit region is decoded to regenerate a difference signal between the second image signal and its prediction signal, and the regenerative prediction signal is added to the difference signal to generate a second regenerative image signal.
In the image decoding method thus constructed, since the regenerative prediction signal of the second regenerative image signal is generated on the basis of the first regenerative image signal which has been subjected to padding processing, the second coded image signal obtained by hierarchically coding the second image signal on the basis of the first image signal, can be hierarchically decoded accurately using the first regenerative image signal.
Further, since, in decoding processing of the second coded image signal corresponding to the target unit region as a target of decoding processing, a signal which is generated on the basis of the first regenerative image signal corresponding to the target unit region is used as its prediction signal, the decoding processing of the second coded image signal merely delays by time for processing the unit region, as compared with decoding processing of the first coded image signal. Therefore, on the basis of the first and second coded image signals which are obtained by hierarchical coding processing of the image signal, a high-resolution image and a low-resolution image can be regenerated almost without a time lag.
According to the present invention (claim 9), in a digital image decoding method as defined in claim 8, the padding processing of the first regenerative image signal corresponding to each unit region comprises replacing the insignificant pixel values in the first regenerative image signal with pseudo pixel values obtained on the basis of significant pixel values in the first regenerative image signal.
In the image decoding method thus constructed, since the padding processing of the first regenerative image signal corresponding to each unit region is performed on the basis of the significant pixel values in the first regenerative image signal, the coded difference signal which is obtained by coding with effectively suppressing the difference between the prediction signal of the second image signal obtained from the first image signal and the second image signal, can be accurately decoded.
According to the present invention (claim 10), a digital image decoding apparatus comprises a first decoding unit for decoding a first coded image signal which is obtained by performing coding processing to a first image signal for forming image space including an image having the arbitrary shape and comprising plural pixels, to generate a first regenerative image signal; and a second decoding unit for decoding a second coded image signal which is obtained by performing coding processing to a second image signal having different resolution from that of the first image signal, for forming image space including the image and comprising plural pixels; wherein the first decoding unit includes first decoding means for performing decoding processing in which a first regenerative image signal is generated from the first coded image signal, to each of unit regions into which the image space is divided; and padding means for performing padding processing in which insignificant pixel values are replaced with pseudo pixel values obtained by a specified method, to the first regenerative image signal corresponding to each unit region; and the second decoding unit includes prediction signal generating means for predicting a second regenerative image signal corresponding to each unit region on the basis of the first regenerative image signal which has been subjected to the padding processing, to generate a regenerative prediction signal; and second decoding means for performing difference decoding processing to each of unit regions, in which decoding processing the second coded image signal corresponding to each unit region is decoded to regenerate a difference signal between the second image signal and its prediction signal, and the regenerative prediction signal is added to the difference signal to generate a second regenerative image signal.
In the image decoding apparatus thus constructed, since the regenerative prediction signal of the second regenerative image signal is generated on the basis of the first regenerative image signal which has been subjected to padding processing, the second coded image signal obtained by hierarchically coding the second image signal on the oasis of the first image signal, can be hierarchically decoded accurately using the first regenerative image signal.
Further, since, in decoding processing of the second coded image signal corresponding to the target unit region as a target of decoding processing, a signal which is generated on the basis of the first regenerative image signal corresponding to the target unit region is used as its prediction signal, the decoding processing of the second coded image signal merely delays by time for processing the unit region, as compared with decoding processing of the first coded image signal. Therefore, on the basis of the first and second coded image signals which are obtained by hierarchical coding processing of the image signal, a high-resolution image and a low-resolution image can be regenerated almost without a time lag.
According to the present invention (claim 11), a digital image decoding apparatus as defined in claim 10 further includes resolution converting means for converting the first regenerative image signal which has been subjected to the padding processing so that its resolution agrees with that of the second regenerative image signal, and outputting a resolution converting signal; wherein the prediction signal generating means comprises prediction means for predicting the second regenerative image signal corresponding to each unit region on the basis of the second regenerative image signal to generate an auxiliary prediction signal; and switching means for performing switching between the auxiliary prediction signal and the resolution converting signal on the basis of control information included in the second coded image signal; and the output of the switching means is output as the prediction signal of the second regenerative image signal corresponding to each unit region.
In the image decoding apparatus thus constructed, since one of the auxiliary prediction signal obtained from the second regenerative image signal and the resolution converting signal obtained from the first regenerative image signal is selected on the basis of the control information included in the second coded image signal, and the selected signal is output as the regenerative prediction signal of the second regenerative image signal corresponding to each unit region, the regenerative prediction signal can be adaptively switched by the simple construction, whereby hierarchical decoding processing corresponding to hierarchical coding processing with more enhanced coding efficiency can be easily realized.
According to the present invention (claim 12), a digital image decoding apparatus as defined in claim 10 further includes resolution converting means or converting the first regenerative image signal which has been subjected to the padding processing so that its resolution agrees with that of the second regenerative image signal, and outputting a resolution converting signal; wherein the prediction signal generating means comprises prediction means for predicting the second regenerative image signal corresponding to each unit region on the basis of the second regenerative image signal to generate an auxiliary prediction signal; and averaging means for weighting and averaging the auxiliary prediction signal and the resolution converting signal; and the output of the averaging means is output as the regenerative prediction signal of the second regenerative image signal corresponding to each unit region.
In the image decoding apparatus thus constructed, since the auxiliary prediction signal obtained from the second regenerative image signal and the resolution converting signal obtained from the first regenerative image signal are weighted and averaged, and the averaged signal is output as the regenerative prediction signal of the second regenerative-image signal corresponding to each unit region, hierarchical decoding processing corresponding to hierarchical coding processing in which the difference between the prediction signal of the second image signal obtained from the first image signal and the second image signal is finely controlled, can be realized.
According to the present invention (claim 13), in a digital image decoding apparatus as defined in claim 12, the padding means is for performing padding processing in which the insignificant pixel values in the first regenerative image signal are replaced with pseudo pixel values obtained on the basis of significant pixel values in the first regenerative image signal.
In the image decoding apparatus thus constructed, since the padding processing of the first regenerative image signal corresponding to each unit region is performed on the basis of the significant pixel values in the first regenerative image signal, the coded difference signal which is obtained by coding with effectively suppressing the difference between the prediction signal of the second image signal obtained from the first image signal and the second image signal, can be accurately decoded.
According to the present invention (claim 14), in a digital image decoding apparatus as defined in claim 10, the first coded image signal is a coded difference signal obtained by compressively coding a difference signal that is a difference between the first image signal corresponding to each unit region and its prediction signal; and the first decoding means comprises a decoder for decoding the coded difference signal; an expander for expanding the output of the decoder to generate a regenerative difference signal; an adder for adding the regenerative difference signal as the output of the expander to the regenerative prediction signal of the first regenerative image signal, and outputting a first regenerative image signal to the padding means; a frame memory for storing the output of the padding means; and a prediction signal generator for generating the regenerative prediction signal of the first regenerative image signal corresponding to each unit region, on the basis of the first regenerative image signal which has been subjected to the padding processing, which image signal is stored in the frame memory.
In the image decoding apparatus thus constructed, since the first regenerative image signal which has been subjected to padding processing is stored in the frame memory, motion compensation in decoding processing can be executed with good precision.
According to the present invention (claim 15), a data recording medium contains a program for making a computer execute coding processing of first and second input image signals having different resolutions, each signal forming image space including an image having the arbitrary shape and comprising plural pixels, the program making a computer execute processes for performing coding processing to each of unit regions into which the image space is divided, in which coding processing the first input image signal is compressively coded to generate a first coded image signal, and the compressed first input image signal is expanded to generated a first regenerative image signal; performing padding processing in which insignificant pixel values are replaced with pseudo pixel values obtained by a specified method, to the first regenerative image signal corresponding to each unit region, and predicting the second input image signal corresponding to each unit region on the basis of the first regenerative image signal which has been subjected to the padding processing, to generate a prediction signal; and performing difference compressive coding to each of unit regions, in which coding processing a difference signal that is a difference between the second input image signal corresponding to each unit region and its prediction signal is compressively coded to generate a coded difference signal, and the compressed difference signal is expanded and the prediction signal is added to the expanded difference signal, to generate a second regenerative image signal.
In the data recording medium thus constructed, since the prediction signal of the second input image signal is generated on the basis of the first regenerative image signal which has been subjected to padding processing, the difference signal which is the difference between the second input image signal having the resolution different from that of the first input image signal and its prediction signal is suppressed, whereby a computer can realize processing of compressing the second input image signal corresponding to the unit region located on the boundary of the object, with suppressing degradation of coding efficiency.
According to the present invention (claim 16), a data recording medium contains a program for making a computer execute processing for decoding first and second coded image signals which are obtained by performing coding processing to first and second image signals having different resolutions, each signal regenerating image space including an image having the arbitrary shape and comprising plural pixels, to generate first and second regenerative image signals, the program making a computer execute processes for performing decoding processing in which a first regenerative image signal is generated from the first coded image signal, to each of unit regions into which the image space is divided; performing padding processing in which insignificant pixel values are replaced with pseudo pixel values obtained by a specified method, to the first regenerative image signal corresponding to each unit region, and predicting a second regenerative image signal corresponding to each unit region on the basis of the first regenerative image signal which has been subjected to the padding processing, to generate a regenerative prediction signal; and performing difference decoding processing to each of unit regions, in which decoding processing the second coded image signal corresponding to each unit region is decoded to regenerate a difference signal between the second image signal and its prediction signal, and the regenerative prediction signal is added to the difference signal to generate a second regenerative image signal.
In the data recording medium thus constructed, the regenerative prediction signal of the second regenerative image signal is generated on the basis of the first regenerative image signal which has been subjected to padding processing, whereby a computer can realize processing of accurately decoding the coded difference signal which is obtained by coding with suppressing the difference between the second input image signal having the resolution different from that of the first input image signal and its prediction signal.